ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07532.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.Fluorescence quantum yield and lifetime measurements of the tyrosine residues in ribonuclease‐A (RNase) were used to study the conformational changes involved in the denaturation of the enzyme. Measurements were done on RNase and on selectively acetylated RNase in the native, the partly denatured (reductive cleavage of S‐S bridges or treatment with 8 M urea) and in the fully denatured state. The data were interpreted to mean that the opening of the S‐S bridges causes large parts of the enzyme chain to unfold while leaving a hydrophobic region; including one of the tyrosine residues, intact. The biological activity of RNase is destroyed by this unfolding. Urea apparently does penetrate the protein coil but does not greatly affect the RNase structure since some of its biological activity is still retained. The opening of the S‐S bridges in the presence of urea destroys the native conformation (and biological activity) completely leaving the protein in the form of an uncoiled polypeptide chain. It is suggested which parts of the protein structure might be affected by partial denat

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07533.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.The luminescent behavior of certain estrogens in the solid state is discussed. Spectra of solid films of estradiol and estriol are red shifted compared to that in liquid solutions with estriol shifted to a lesser extent. The red shifts are attributed to intermolecular hydrogen bonding, this conclusion being based on IR spectra and X‐ray data. The calculated distance over which hydrogen bonding takes place is 2.755 Å in estradiol and 2.638 Å in estriol. The increased shift in the spectrum of estradiol is believed to be due to an additional hydrogen bond with a water molecule present in the solid film (O—O distance 2.793 Å). In estrone the weak fluorescence present in liquid solution is absent in solid film, in contrast to 3‐desoxyestrone where fluorescence is preserved. Out of three possible forms of crystalline estrone only two can form hydrogen bonds, based on O‐O distance calculations. In equilenin, which is highly fluorescent in liquid solution, no fluorescence is detected in solid film. This again is attributed to hydrogen bonding between the hydroxyl group of the β‐naphtholic chromophore and the carbonyl group in the C(17) position. Dihydroequilenin which lacks the carbonyl group and equilenin dissolved in a host crystal retain their

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07534.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.Proflavine‐mediated photoinactivation of φ times 174 phage and its isolated DNA was studied under identical irradiation conditions. The inactivations followed single‐hit kinetics and a linear relationship was obtained in reciprocal plots of the inactivation rates vs the proflavine concentrations for both phage and isolated DNA. The phage photoinactivation rate was increased with an increase in the amount of proflavine bound to the phage DNA in a strong binding range (0.01‐0.04 proflavine/ nucleotide) as the total proflavine concentration was increased or the ionic strength decreased. Further, a phage‐specific factor was also found to affect the inactivation rate. The photodynamic treatment induced mutations in three phage strains from “amber” to “wild type” at a mutation rate per lethal hit of 0.3 times 10‐5to 2.6 times 10‐5. In contrast to phage infectivity, the φ times 174 DNA infectivity was measurable only at a high multiplicity of infection, and its photoinactivation occurred only at high proflavine concentrations. The photoinactivation rate was enhanced either with a decrease in the multiplicity of infection or with the use of spheroplasts ofrecAmutants strains. The results are discussed in terms of the nature of and possible repair mechanisms of photodynamically induced lesions in

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07535.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.In view of the recent interest in the possibility of a singlet oxygen mechanism playing an important role in photodynamic action, a number of different types of dyes were surveyed with respect to cell inactivation and induction of genetic changes in yeast cells. These comprise three xanthene dyes, three thiazine dyes, three acridine dyes and ethidium bromide. Rhodamine B in the first group and methylene blue in the second group were inactive under the present conditions. Both were found to be non‐penetrable into the cell. However, since toluidine blue is active, non‐penetrability is not a determining factor in photodynamic action. Ethidium bromide was inactive under the present conditions, even though it was penetrable into the cell. The survey showed that the dye must be bound to DNA in order to be active in the induction of a genetic change (gene conversion). All dyes which were active in either inactivation or induction or both were modified in their effectiveness both by the addition of N‐3(suppression) and in deuterated medium (enhancement), indicating that the sensitization mechanism involves singlet oxygen. The deuterium effect was generally observable to a lesser extent in thein vivosituation thanin vitro, in particular for genetic changes by profiavine and acriflavine in which the sensitizer binds t

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07536.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.Irradiation of Dulbecco's modified Eagle's tissue culture medium with “Daylight,”“Special Blue,” or “Bilirubin” fluorescent light produces photoproducts lethal to human cells. Killing is abolished when (1) riboflavin, (2) tryptophan and tyrosine, or (3) riboflavin, tryptophan and tyrosine are deleted from medium prior to irradiation with any of the above fluorescent lamps. Toxic photoproducts are also formed when buffered salt solutions containing (a) riboflavin and tryptophan, (b) riboflavin and tyrosine, or (c) riboflavin, tryptophan and tyrosine are exposed to any of these li

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07537.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.The triplet‐triplet absorption of all‐trans and 11‐cisretinal was measured as a function of the exciting radiation from 423 nm to 365 nm in a glass of 3‐methylpentane at 77 K. This experiment was also accomplished with all‐trans retinal in hexane at ambient temperature. The relative triplet formation quantum yields of all‐trans and 11‐cis retinal at 77 K were found to be independent (±10%) of the frequency of the exciting radiation. At room temperature we measured an increase in this relative quantum yield for all‐transretinal from 1.0 at 365 nm to 1.82 at 423 nm [Bensassonet al.(1975) measured an absolute quantum yield of 0.45 at 353 nm]. These results are used to evaluate previous interpretations for photophysical decay processes in all‐trans retinal, and previous suggestions for wavelength dependent radiationless transitions are shown to be unacceptable. High energy excitation of 300 K solutions of all‐transretinal produce excited states that result in less efficient intersystem crossing. These states appear to be inaccessible in the 77 K matrices. We suggest that steric restrictions introduced by the retinal matrix interaction at 77 K are able to block this new internal conversion pathway back

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07538.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.Nanosecond flash photolysis of rhodopsin with 530 or 353 nm light produces an initial transient absorption spectrum with peaks at ˜57O and ˜420nm, and a subsequent transient species with a maximum absorption at 480 nm. These results are interpreted as the initial formation of prelumi‐rhodopsin (570 nm) followed by its conversion to lumirhodopsin (470 nm). The peak at 420 nm in the first transient may be due to either hypsorhodopsin or isorhodop

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07539.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.The quinone antagonist dibromothymoquinone (2,5‐dibromo‐3‐methyl‐6‐isopropyl benzoquinone, DBMIB)‡ was used to inhibit early photochemical changes in chromatophores of the photo‐synthetic bacterium,Rhodospirillum rubrum.With continuous illumination with near infrared light, we observed an approximately threefold decrease in efficiency of P865+formation at 100–200 μM DBMIB as measured by absorbance changes at 605 or 430 nm. However, with continuous illumination of several seconds duration, maximal absorbance changes were observed. At low concentrations (1–10 μM) of DBMIB, a decrease in the decay rate of the ΔA430or ΔA605was observed. Using a short (2–10 μs), low intensity light pulse for excitation, we observed that DBMIB inhibits P865+formation. The concentration dependency of this inhibition corresponds to that seen with continuous illumination. We tested the possibility that DBMIB was displacing the first stable electron acceptor, which has been shown to be a tightly bound ubiquinone (UQ) inR. rubrum.Chromatophores prepared from cells grown with14C‐p‐hydroxybenzoic acid in their media provided a sample in which the benzoquinones were labelled specifically with14C. These labelled chromatophores were first extracted with petroleum ether to remove the loosely bound ubiquinone pool and then were treated with DBMIB. DBMIB displaced about 1/2 of the remaining tightly‐bound UQ present. The DBMIB inhibition was tested for reversibility by adding an excess of UQ to DBMIB‐treated samples. In these cases, restoration to 80% could be achieved from samples which were only 20% active relative to the untreated samples. A similar inhibitory effect by DBMIB was also demonstrated in whole cells ofRhodospirillum rubrum, the G‐9 mutant ofRhodospirillum rubrum, Rhodopseudomoms sphaeroides, Rhodopseudomonas capsulata, andChromatium vinosum.The mechanism for inhibition is most consistent with displacement of, or interference with the first stable electron acceptor (ubiquinone) rather than by random quenching of excited states at the le

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07540.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract.The delayed light emission decay rate (up to 120 μs) and the rise in chlorophyllafluorescence yield (from 3 to 35 μs) in isolated chloroplasts from several species, following a saturating 10 ns flash, are temperature independent in the 0–35°C range. However, delayed light in the 120–340 μs range is temperature dependent. Arrhenius plots of the exponential decay constants are: (a) linear for lettuce and pea chloroplasts but discontinuous for bush bean (12–17°C) and spinach (12–20°C) chloroplasts; (b) unaffected by 3‐(3,4 dichlorophenyl)‐1,1‐dimethylurea (inhibitor of electron flow), gramicidin D (which eliminates light‐induced membrane potential) and glutaraldehyde fixation (which stops gross structural changes).The discontinuities, noted above for bush bean and spinach chloroplasts, are correlated with abrupt changes in (a) the thylakoid membrane lipid fluidity (monitored by EPR spectra of 12 nixtroxide stearate, 12NS) and (b) the fluidity of extracted lipids (monitored by differential calorimetry and EPR spectra of 12 NS). However, no such discontinuity was observed in (a) chlorophyllafluorescence intensity of thylakoids and (b) fluorescence of tryptophan residues of delipidated chloroplasts.Microsecond delayed light is linearly dependent on light intensity at flash intensities as low as one quantum per 2 times 104chlorophyll molecules. We suggest that this delayed light could originate from a one quantum process in agreement with the hypothesis that recombination of primary charges leads to this light emission. A working hypothesis for the energy levels of Photosystem II components is proposed involving a charge stabilization step on the primary acceptor side, which is in a lipid environment.Finally, the redox potential of P680 (the reaction center for chlorophyll of system II) is calculated to

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07541.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY